1. Field of the Invention
The present invention relates to a fuel control system of the type in which an electromagnetic valve responsive to timing pulse voltage is employed to intermittently open and close the passage for supplying fuel, whereby to control particularly the quantity of fuel delivered to the combustor of a gas turbine engine. U.S. Pat. No. 2,980,090 (Sutton et al) and U.S. Pat. No. 3,515,104 (Reichart) are the related patents which disclosed the prior art with which the present invention is concerned.
2. Description of the Prior Art
In known intermittent fuel metering systems of the type which employ an electromagnetic valve, the repetition period of timing pulses for opening the electromagnetic valve is varied in accordance with an engine operating parameter such as the rotational speed of the engine.
A disadvantage of this type of known system is that if it is used with an engine such as a gas turbine wherein the burning of fuel and air in the combustor is effected continuously, when the engine is in the low rotational speed range and the operating conditions are such that the quantity of the fuel delivered is small, the duration of the time when the electromagnetic valve is opened and fuel is delivered to the combustor is reduced and the duration of the time when the electromagnetic valve is closed is increased with the result that the pulsating of the fuel delivered to the combustor through the electromagnetic valve increases considerably thus failing to ensure a satisfactory burning in the combustor. This results in the generation of an abnormal combustion noise and further in the occurrence of misfiring if the pulsating of the fuel is very great. In this case, while the provision of for example a pressure damper in the fuel passage leading from the electromagnetic valve to the fuel injection nozzle of the combustor has the effect of reducing the pulsating of the fuel injected, there is a disadvantage in that the follow-up of the fuel injection quantity to the variation of the flow rate due to changes in the operating conditions is deteriorated by the fuel accumulating action of the pressure damper. Another disadvantage of the known system is that in the case of an automobile turbine having a wide range of variation for the rotary speed of the engine, if the repetition frequency of timing pulses for actuating the elctromagnetic valve in one engine rotary speed range is selected so high that the occurrence of the above-mentioned abnormal burning is prevented, the repetition frequency of the timing pulses tends to become excessively large in the higher rotary speed range with the result that the electromagnetic valve finds it difficult to conform with such a high repetition frequency and hence it is impossible to meter the fuel with high accuracy.